The electrophoretic display device is configured to generate an image by moving a charged particle (floating particle) for each pixel. The electrophoretic display device may be formed into a thin and light-weight structure with less power consumption. Unlike the liquid crystal display device, the electrophoretic display device employs no polarization plate, which is advantageous in view of brightness. The device further ensures to keep high contrast when it is used outdoors.
Various types of electrophoretic display device have been developed. Japanese Unexamined Patent Application Publication No. 2007-47208 discloses an electrophoretic display device which generates an image by moving floating particles between a flat electrode and a partition electrode for each pixel. According to the document, the resistance film with a sheet resistance ranging from 102Ω to 1015Ω is used as the electrode which attracts the floating particles so as to accelerate movement thereof and increase the response speed.
Japanese Unexamined Patent Application Publication No. 2008-83450 discloses an electrophoretic display device configured to control brightness of each pixel by attracting negatively charged white floating particles or positively charged black floating particles to the electrode of the upper substrate under control of the voltage applied thereto so as to generate images.
The electrophoretic display device according to the present invention is configured to have a flat electrode to which the black floating particle is adhered for black display and a partition electrode to which the black floating particle is adhered for white display for each pixel so as to generate the images.
For the display which includes the flat electrode to which the black floating particle is adhered for black display, and the partition electrode to which the black floating particle is adhered for the white display for each pixel so as to generate the image, it is necessary to make the partition electrode area the same as the flat electrode area in order to give sufficient memory property to the image.
Once the floating particle adheres to the flat electrode or the partition electrode, the electrophoretic display device exhibits the memory effect so that its state is retained even if application of the voltage to the respective electrodes is interrupted. Unlike the liquid crystal display device, the electrophoretic display device is not required to keep the pixel electrode at the predetermined voltage for retaining the predetermined state, thus being advantageous in view of power consumption.
For giving the device sufficient memory property, the partition electrode area has to be the same as the flat electrode area. For this, height of the partition has to be increased. If the partition height is increased, its strength may be insufficient, thus requiring increase in the partition width. That is, the partition configured to define the distance between the TFT substrate and the sealing substrate is required to exhibit predetermined strength. If the partition width is increased, the occupancy of the flat electrode for generating the image in each pixel is reduced, resulting in deteriorated screen brightness. Japanese Unexamined Patent Application Publication No. 2007-47208 does not disclose the problem relevant to the flat electrode area and the partition electrode area.